DESCRIPTION: (Applicant's Abstract) Cocaine tends not to be immediately addictive. Current estimates place the percentage of persons in the United States who have become dependent on cocaine at about 7% (more than 2 million individuals so far) of those who ever use the drug. The factors that lead to dependence have not been identified, but clinical evidence suggests that a prolonged period of intermittent use of the drug often precedes the development of dependence. The proposed research is aimed at furthering our knowledge concerning behavioral effects of relatively long-term intermittent exposure to cocaine. Laboratory study of effects of long-term intermittent exposure to cocaine has yielded a puzzling array of results. Sometimes tolerance is observed, sometimes sensitization.. Previous research, however, has indicated that experiential/behavioral factors can determine whether or not tolerance occurs to cocaine's effects. The proposed research is aimed at adding to our knowledge of how experiential factors interact with repeated cocaine exposure. The specific aims of this application are to: 1.) Continue analyses of dose and dose variability in effects of repeated exposure to cocaine. 2.) Perform analyses of conditions in which tolerance develops to response-rate and reinforcement-rate increases produced by cocaine. 3.) To determine if reinforcement-schedule-parameter dependent tolerance is ~contingent" tolerance and if it is environment specific. 4.) Determine if reinforcement-schedule-parameter-specific tolerance is predictable from the behavioral economics involved. 5.) Study the role of an instrumental contingency in the determination of tolerance or sensitization to effects of repeatedly experienced cocaine. The study of long-term, intermittent exposure to cocaine has potential relevance to the genesis of cocaine dependence. Understanding of the processes that occur under long-term, intermittent exposure should facilitate the development of effective treatment and, especially, prevention programs.